“White smells” are to odors what white noise is to sound

Over-saturating your olfactory nerves is a good way to smell nothing.

The featureless soundscape known as white noise is effectively as neutral as music can get for humans—too many frequencies are combined in one waveform and the human ear just isn't able to pick any specific detail out. The same thing happens with white light, which contains all the colours of the visual spectrum. Now it seems that it's possible to create "white smells"—that is, smells that don't smell of anything specific.

White noise isn't just a hum in the background—it specifically refers to a kind of frequency spectrum that's completely flat (and Wired.co.uk has previously explored the different "colors" of sound). Every frequency has the same energy, so the noise just kind of melts into an overall hum of nothingness. White smell works on the same principle. Neurobiologists from the Weizmann Institute of Science, led by Tali Weiss, managed to create something they call "Laurax." And there are several different versions of Laurax, each chemically different, but they each smell "white."

Weiss and her team first derived a range of 86 "monomolecular odorants" which covered the effective spectrum of smell. Each one was diluted to the same odor intensity (so no one smell would overpower any other), and then mixed together into a range of batches containing either "one, four, ten, 15, 20, 30, 40, or 43 components." An algorithm worked out how to make sure that the molecules that were mixed into each batch were consistently spread far apart from each other across the smell spectrum so as to ensure there wasn't smell overlap.

That left them with 191 individual batches for their 56 study participants to have a sniff at. Unsurprisingly, when a batch with only one component, or four components, was compared to a batch with a similar small number of components, the differences were easy to detect. But, importantly, as the number of components in the batch increased, it became harder and harder for the participants to tell the difference between the smells of each batch. And, when comparing batches with 30 or more components, the difference was impossible to discern for most participants.

Even more intriguingly, those batches didn't share common components, yet still smelled the same. It appeared that those batches had gained some quality of whiteness simply from having lots of ingredients. However, Weiss writes: "This trend implies that if more and more non-overlapping components are added to each of two mixtures, these two mixtures eventually should smell the same, despite having no components in common. Indeed, given a sufﬁcient number of equal-intensity spanned components, this trend implies that eventually all mixtures should smell the same. We call this predicted ultimate point of perceptual convergence 'olfactory white.'"

They double-checked their results using the Laurax name—they created four new mixtures with 40 components each, each labelled "Laurax" (a meaningless word designed to "avoid any cognitive influences of the word 'white'"). They asked the participants to get used to the smell of their Laurax over three days, and on the fourth day they were given a new mixture and asked whether it was also a batch of Laurax. As expected, the more components there were in the new mixture, the more likely the participants were to label it Laurax, even if it had none of the same ingredients.

So what does Laurax, or "olfactory white," smell like? Weiss describes it as "intermediately pleasant and edible," which is perhaps almost as vague a description as can be imagined. The terms the participants used to describe Laurax were all similarly vague—the study (published in The Proceedings of the National Academy of the United States of America) includes the suggestions from the participants, like "mouse-like," "eggy," "fruity," "spicy," "medicinal," and even "sweet." It seems to smell like pretty much everything, and that's why it doesn't smell like anything at all—our nasal sense is overwhelmed across such a wide spectrum that it can't pick out one individual note of smell.

Smells like Laurax don't exist in nature, Weiss explains, even though lots of smells (like coffee, or dirty socks) are made up of lots of components. It's just that those components are usually either very similar, instead of spread out across the smell spectrum, or there's one smell that overpowers the rest.

Nevertheless, olfactory white has some potential practical use—it can, Weiss says, be used to cover up other smells. Strong smells—like rose—which were mixed in with Laurax, just smelled to a small group of participants like... Laurax. That could be good news for people who hate the smell of disinfectant, or for manufacturers of smell-covering products.

Every time I think I smell something burning, especially a faint electrical-burn smell, I start sniffing around trying to find the source. Next thing I know, I can't smell anything. Maybe it's just me, but I find it very easy to overwhelm my olfactory sensors.

We've known this for eons, just spend a while in the restroom after thanksgiving!

An interesting side note, it sounds like they basically made a Jägermeister of smells in a neutral space. (i.e. Jäger is a mixture of some 37..i think... different herbs and spices and doesn't have an identifiable flavor like other liqueurs)

Every time I think I smell something burning, especially a faint electrical-burn smell, I start sniffing around trying to find the source. Next thing I know, I can't smell anything. Maybe it's just me, but I find it very easy to overwhelm my olfactory sensors.

Certain types of foods do that too me as well. Vietnamese food is one of them...

Every time I think I smell something burning, especially a faint electrical-burn smell, I start sniffing around trying to find the source. Next thing I know, I can't smell anything. Maybe it's just me, but I find it very easy to overwhelm my olfactory sensors.

Awesome article--made me think of smells in a while new way. I wonder what implications this has for brains in general. Could we have "white thoughts"? Something like meditation, or the opposite of meditation. I guess that's not really closely related to receptors, but if we confused the neurons in a similar way...

I wonder if chemists are going to start whipping up laurax-scented household products some time soon...

An interesting side note, it sounds like they basically made a Jägermeister of smells in a neutral space. (i.e. Jäger is a mixture of some 37..i think... different herbs and spices and doesn't have an identifiable flavor like other liqueurs)

Jäger has a VERY distinct flavor, so I have no idea what you're talking about.

I wonder what the long-term effects of Laurax exposure might be. This could have a definite downside - if our sense of smell is constantly stimulated by Laurax but we have no perception of it, would that deaden our perception to its constituent smells? Would it be like hearing, which can be harmed by constant overstimulation, or like sight, where there's no downside to relatively constant bright light exposure (as far as I know) and the eye can rapidly adjust from bright to dark environments?

An interesting side note, it sounds like they basically made a Jägermeister of smells in a neutral space. (i.e. Jäger is a mixture of some 37..i think... different herbs and spices and doesn't have an identifiable flavor like other liqueurs)

Jäger has a VERY distinct flavor, so I have no idea what you're talking about.

It's possible he was trying to claim that the flavour of any particular herb or spice cannot be identified within Jägermeister.I would take issue with that, since I've always thought anise was pretty dominant in the drink.

Since they are aiming for a broad spectrum of equal intensity, it seems like they could get better mileage to cover up bad smells by leaving gaps in the spectrum where particular foul odors would fill in (and thus equalize).

I remember a friend of mine's dogs coming in from outside once after being sprayed by a skunk. They were foaming at the mouth and tried to rub it off on everything. After a half hour or so we thought the smell had gone. A little later another friend shows up and wouldn't even enter the house due to the smell....which we thought had already gone away!

In addition to drug dogs, I would suspect it might also prove useful in fooling bomb sniffing dogs, bloodhounds, and animals like deer that are being hunted, although I'm not sure if in the latter case it wouldn't scare them off.

The authors diluted their component odorants to 'a point of about equal perceived intensity' (emphasis added). Strictly speaking, the closest auditory analogue is therefore grey noise, which is white noise that has been shaped by the perceptual loudness function, and is the type of noise in which all frequencies will be perceived to have roughly equal intensity. You can compare different 'colours' of noise on the Wikipedia page - white noise clearly has more prominent frequencies in the upper mid-range, simply because we're more sensitive to those.

The authors diluted their component odorants to 'a point of about equal perceived intensity' (emphasis added). Strictly speaking, the closest auditory analogue is therefore grey noise, which is white noise that has been shaped by the perceptual loudness function, and is the type of noise in which all frequencies will be perceived to have roughly equal intensity. You can compare different 'colours' of noise on the Wikipedia page - white noise clearly has more prominent frequencies in the upper mid-range, simply because we're more sensitive to those.

It really seems to me that the color names for sound are rather arbitrary. White light would need to be balanced for our perceptions as well in order to be white, so technically grey noise is analogous to white light. It seems that they are saying that white noise must be perfectly balanced (and thus sound high pitched) while white light balanced in the same way would probably appear green.

Also, white/grey/black are all the same really. And if you don't really believe this think about how "black" the black letters on a projector screen really are considering that without the projector shining on it you'd consider the screen to be white.

The authors diluted their component odorants to 'a point of about equal perceived intensity' (emphasis added). Strictly speaking, the closest auditory analogue is therefore grey noise, which is white noise that has been shaped by the perceptual loudness function, and is the type of noise in which all frequencies will be perceived to have roughly equal intensity. You can compare different 'colours' of noise on the Wikipedia page - white noise clearly has more prominent frequencies in the upper mid-range, simply because we're more sensitive to those.

White light has to be balanced for human perception as well or I'd assume it would appear green.

It seems to me the color labels for noise are rather arbitrary since grey/white/black are all the same spectrum-wise.

moheeb wrote:"I remember a friend of mine's dogs coming in from outside once after being sprayed by a skunk. They were foaming at the mouth and tried to rub it off on everything. After a half hour or so we thought the smell had gone. A little later another friend shows up and wouldn't even enter the house due to the smell....which we thought had already gone away!"

I was a psych major in college. I remember a pretty interesting stimulus-response phenomena regarding this kind of occurrance. When our senses are introduced to a new stimulus (the skunk smell in this case), olfactory neurons start firing in response to the stimulus, and this, in effect, gives us the ability to smell the bad smell. Over a period of time, the neurons become over stimulated and slow down their firing response and in effect, we become "used to the smell." The smell is still there but you perceive it is gone because your olfactory neurons aren't firing in response to it anymore. So, a new person enters the scenario and the cycle starts again, with his olfactory neurons firing in response to the smell. The new person can smell it, but you can't because you have been there for a while.

I may be mis-stating some of the more technical aspects of it, but that's the jest of what I remember. I thought it was interesting, anyhow.

Every time I think I smell something burning, especially a faint electrical-burn smell, I start sniffing around trying to find the source. Next thing I know, I can't smell anything. Maybe it's just me, but I find it very easy to overwhelm my olfactory sensors.

What you are describing is adaptation, it's not the same thing at all. When something in your environment isn't changing (e.g. a background smell) then you brain stops paying attention to it. So if you are in a room that smells faintly and unchangingly of smoke, after a while, you don't notice the smoke any more.

the suggestions from the participants, like "mouse-like," "eggy," "fruity," "spicy," "medicinal," and even "sweet." [...] olfactory white has some potential practical use—it can, Weiss says, be used to cover up other smells.

I smell the ultimate deodorant here, if most people find it pleasant. You still would want some antiperspirant against the moist, but the other effects may be well "buffered".